1. Field of the Invention
The present invention relates generally to hybrid drive-train systems for motor vehicles and more particularly to a method and apparatus for determining the torque required to launch the vehicle and for controlling operation of the hybrid drive-train in accordance with the required torque.
2. Description of the Related Art
A direct hybrid drive-train system typically includes a reduced capacity internal combustion engine, such as a diesel engine, which is operated in parallel with a second prime mover, such as an electric or hydraulic motor. Compared to the internal combustion engine employed in a conventional vehicle drive-train system, i.e., a drive-train system employing only an internal combustion engine, an internal combustion engine in a hybrid drive-train system has a reduced torque output capacity because its output may be supplemented by the second prime mover. Accordingly, a hybrid drive-train system has a limited ability to launch the vehicle using one prime mover independently of the other, particularly when the vehicle is being launched on a grade. To maintain the ability to launch a hybrid vehicle in a variety of operating conditions, particularly when only one of the prime movers is active, it would be beneficial to first determine the torque required to launch the vehicle. The torque required to launch the vehicle could then be used to determine whether the engine and the motor would be operated simultaneously to launch the vehicle.
There are several vehicle operating conditions which influence the torque required to launch a vehicle. The conditions that have a major impact are, the gross combined vehicle weight (GCW) and the grade or inclination of the road surface upon which the vehicle is resting. When these two major conditions are known, it is possible to identify the wheel torque required to launch the vehicle. While the grade of the road surface can be measured directly with an inclinometer, GCW is not readily available.
Automated vehicular systems using GCW as a control parameter and/or having logic for determining GCW may be seen by reference to U.S. Pat. Nos. 5,272,939; 5,335,566; 5,487,005 and 5,490,063, the disclosures of which are incorporated herein by reference. A system for resetting the highly filtered value of GCW upon sensing conditions indicative of the vehicle being at rest and/or the highly filtered value (GCWCP) differing from a less-filtered test value (GCWTEST) by greater than a predetermined value may be seen by reference to U.S. Pat. No. 5,491,630, the disclosure of which is also incorporated herein by reference in its entirety.